"Glenn" Spaketh Thusly:

It is a protein build-up. It comes from the food, and from the fish. It is
normal. A little surface agitation will suspend it in solution for
filtration. People who use hob filters like aquaclear do not see this
because the filter agitates the surface. If you do not want to agitate
(due, lets say to plants needing the extra CO2) you can float a single sheet
of newspaper or even a paper towel for just 30 seconds or so, and it will
absorb the layer. When I do my water changes with the python system, I
invert the nozzle and "slurp" the water from the surface. This skims it off
nicely.
I get the same thing. I skim it off with an extra large plastic cup before I
do my water changes if it's a vacuuming week. Otherwise it comes out as I
scoop the water out.

A while back someone mentioned here that platys will eat it. I've never had
one so I can't say how well that works.

--
Bill H. [my "reply to" address is real]
www.necka.net
Molon Labe!